linux-kernel - Re: [PATCH v4 3/7] vmalloc: Add text_alloc() and text

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Message-ID: <20200723222835.GC12405@linux.intel.com>
Date:   Fri, 24 Jul 2020 01:28:35 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>
Subject: Re: [PATCH v4 3/7] vmalloc: Add text_alloc() and text_free()

On Sat, Jul 18, 2020 at 07:23:59PM +0300, Mike Rapoport wrote:
> On Fri, Jul 17, 2020 at 06:04:17AM +0300, Jarkko Sakkinen wrote:
> > Introduce functions for allocating memory for dynamic trampolines, such
> > as kprobes. An arch can promote the availability of these functions with
> > CONFIG_ARCH_HAS_TEXT_ALLOC. Provide default/fallback implementation
> > wrapping module_alloc() and module_memfree().
> > 
> > Cc: Andi Kleen <ak@...ux.intel.com>
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > ---
> >  include/linux/vmalloc.h | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> > 
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index 0221f852a7e1..e981436e30b6 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -9,6 +9,7 @@
> >  #include <asm/page.h>		/* pgprot_t */
> >  #include <linux/rbtree.h>
> >  #include <linux/overflow.h>
> > +#include <linux/moduleloader.h>
> >  
> >  #include <asm/vmalloc.h>
> >  
> > @@ -249,4 +250,26 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> >  int register_vmap_purge_notifier(struct notifier_block *nb);
> >  int unregister_vmap_purge_notifier(struct notifier_block *nb);
> >  
> > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
> > +/*
> > + * Allocate memory to be used for dynamic trampoline code.
> > + */
> > +void *text_alloc(unsigned long size);
> > +
> > +/*
> > + * Free memory returned from text_alloc().
> > + */
> > +void text_free(void *region);
> > +#else
> > +static inline void *text_alloc(unsigned long size)
> > +{
> > +	return module_alloc(size);
> > +}
> > +
> > +static inline void text_free(void *region)
> > +{
> > +	module_memfree(region);
> > +}
> 
> Using module_alloc() as the default implementation of generic
> text_alloc() does not sound right to me.
> 
> I would suggest rename module_alloc() to text_alloc() on x86, as Peter
> proposed and then add text_alloc_kprobes() that can be overridden by the
> architectures. x86 could use text_alloc(), arm64 vmalloc() with options
> of their choice and the fallback would remain module_alloc(). Something
> like (untested) patch below:

I'm not exactly sure which of the below is relevant as the patch set
includes the exact same changes with maybe different phrasing:

https://lore.kernel.org/lkml/20200717030422.679972-1-jarkko.sakkinen@linux.intel.com/

If there is something that these patches are missing, please do remark
but these seven patches have been at least tested and split in
reasonable manner.

/Jarkko